Hypothalamo-pituitary neurosecretory system of the Northern redbacked vole Clethrionomys rutilus in the course of population cycle

Hypothalamo-pituitary neurosecretory system (HPNS) of the Northern redbacked vole, Clethrionomys rutilus was studied at different stages of the population cycle using paraldehyde-fuchsin staining and immunohistochemical revealing of vasopressin and oxytocin. We found at the stages of high voles number (peak and recession), an increase of vasopressin synthesis in the neurosecretory cells (NSC) of paraventricular (PVN) and supraoptic (SON) nuclei, as well as its active transport and release to the portal capillaries of the outer zone of median eminence (ME). At the stages of low voles number (depression and growth) was demonstrated that level of oxytocin synthesis in the NSC of SON was high and moderate in the NSC of PVN, which was accompanied by an extensive release of oxytocin to capillaries of the posterior pituitary (PP). Increased supply of vasopressin to portal blood flow of the vole pituitary in conditions of overpopulation is suggested to have highly stimulating influence on adrenocorticotropic function of pituitary, which negatively affects the reproductive function of the voles and leads to a decrease of their number. At the stages of low number of population in conditions favoring the life of the voles, the increased supply of oxytocin to the systemic blood flow stimulates the reproductive behavior of the voles, which results in rise of their population during this period.